Method and apparatus for testing the folding endurance of paper and like materials



NOV. 7, 1939. J CLARK v 2.179.116

METHOD AND APPARATUS FOR TESTING ,THE FOLDING ENDURANCE OF PAPER ANDLIKE MATERIALS Filed March 13, 19:57

2 F76, 8. #769. 06/0. F/a/fi H612.

E1] in g 3 um INVENTOR Patented Nov. 7, 1939 LIKE MATERIALS James dA.Clark, Rose Valley, Pa.

Application March 13,

6 Claims.

This invention relates to a method and apparatus for determining thefolding quality of paper, textiles and like materials.

l'n the principal form of apparatus hitherto employed for this purposethe test strip of material is. clamped between a pair of jawswhich canslide towards each other against the tension of two springs. The centreof this strip passes through a thin slotted member which is ar- 1cranged to oscillate back and forth on a plane at right angles to that ofthe strip. As the slotted member moves from its centre position it pullsthe test strip between and round a pair of guide rollers, bending orfolding the strip round Li a small radius at one edge of slot. Meanwhilethe clamping jaws move toward each other maintaining and increasing thetension on the strip.

The slotted member then returns to its central position and moves beyondit between a second of guide rollers, folding the strip in reverseacross the opposite edge of the slotted member.

This cycle continues until the strip breaks and the number of cycles ordouble folds thus com 'pleted before fracture is counted.

While the above mechanism has been in use for many years it has not beenentirely satisfactory as the results vary unpredictably, particu- 'larlybecause of uncertainty as to the tension. of the springs and also thefriction of theguide 34) rollers. To overcome the disadvantages of theguide rollers another form of test instrument was later devisedembodying several simplifications. 'In this second apparatus the teststrip is clamped vertically between two jaws, the upper one of 1,;which, by means of a spring, is arranged to apply any desired tension tothe strip while the lower jaw is wedge shaped and oscillates through 270about its apex in which the strip is inserted. The outer wedge shapededges of the lower jaw clamps are radiused and the strip is bent undertension round each radiused edge of the jaw as it oscillates, until thestrip breaks. It has been found almost impossible in practice toconstruct and maintain the radiused edges and the axis of rotation to apreselected standard, so that test strips are equally affected indifferent instruments or in the same instrument after some wear hasoccurred; which prevents the rigid stand ardization of test results,especially when carried 50 out with different instruments.

The principal object of the present invention is to provide an improvedmethod for testing the folding quality of paper, and like materials,which more nearly simulates the forces imposed 55 on the material duringcommon usage and to 1937, Serial No. 130,669

provide a simple apparatus which may be readily and exactly calibratedso as toensure constancy in the test results among differentinstruments.

Another object is to provide a simply construted and compact apparatusto test a number -15 of specimen strips simultaneously, thus enabling anaverage test result to be quickly ascertained.

Other objects and advantages of the invention will be apparent from thedrawing, from the description thereof and from the claims.

In the drawing:

Fig. 1 illustrates a diagrammatic front View of one form of theapparatus.

Fig. 2 shows an enlarged view of the catch I2 shown on Fig. l forreleasing the arm of the counter as soon as the strip breaks.

Figs. 3 to 12 show ten successive steps in the position of the jaws andoscillating pins and the folding of the paper sample.

In this invention, the strip of material to be tested is folded overitself along a line, preferably at right angles, to the length of thestrip. The fold. so made is subjected to a predetermined pressure; thestrip is then unfolded and subjected to a predetermined tension, whichis less than that required to break an uncreased strip, then the stripis folded again about the same line, either in the samemanner as beforeor else folded in the reverse way about the same line, the fold againsubjected to the same pressure, the strip unfolded, subjected to thesame tension and this cycle of operations repeated until the stripbreaks at the fold. The number of folds so made before the strip breaksis recorded as the folding test of the material. I

In its simplest form, the apparatus required to carry the invention intoeffect comprises any suitable clamp having a weight less than thetensile breaking load of the strip and which may be attached to one endof the test strip, another weight of any convenient shape having as itsbase, a plane surface wider than that of the fold to be made in the teststrip and another plane surface on which to rest the folded sample andthe weight. The weighted clamp is fixed to one end of the test strip andwith the fingers, the strip is doubled about itself to form a fold,which is laidon the plane surface and the weight is gently placed uponthe fold so as to apply pressure to it. The weight is then removed andthe free end of the strip is raised vertically with the fingers untilthe creased strip bears the weighted clamp in tension. The tension isreleased and the strip is refolded about the crease in the same or inthe reverse direction, pressed between the plane surface and the weight,and

the free end of the strip raised till it is again in tension and thiscycle repeated till the strip breaks at the crease, the number of foldsso made before fracture, being counted.

A form of apparatus to carry out this procedure automatically, is shownin Fig. 1 where the strip of material to be tested, I, is clampedbetween a lower jaw 2 and upper jaw 3. The upper jaw assembly 3 isconstrained to move vertically in guide 4 and at its tip is fixed aweight 5 so dimensioned that its weight and that of the moving parts ofthe jaw assembly is a fixed amount, for example, 1 kilogram. The weightof this assembly is normally supported on the adjustable screw 6.

The lower jaw assembly 2 is constrained to move vertically betweenflanged or grooved guide rollers 'I. The lower end of the assembly, inthe absence of the test strip rests continually on an eccentric, almostcircular shaped, cam 8, which is rotated at a suitable speed, forexample '75 revolutions per minute, by a motor 9.

On the jaw assembly 2 is provision for holding 5 one or more slottedweights 13 so that the weight of the lower jaw assembly which, forexample without added weights is adjusted to be exactly kilogram, may beincreased in successive steps by added weights to become 4 kilograms.The centre of gravity of the weights l3 and also the entire lower jawassembly are each arranged to be vertically beneath and in the centre ofthe test strip I, so that the guide rollers 1 are not subjected to anylateral pressure, so that by providing a very small clearance betweenthe jaw assembly and each pair of rollers, any friction they might have,does not affect the tension in the test strip as produced by the weightof the lower jaw assembly.

The test strip l, is of such a length that when clamped between the jawsit supports the lower jaw assembly in such a position that when the topof cam 8 is in its lowest position, as illustrated in Fig. 1, there is asmall distance between the bottom of the lower jaw assembly and the faceof the cam 8. As the cam rotates it touches the assembly and then raisesit until the faces or anvils of the two jaws meet and the upper jaw justraised off the stop 6. The horizontal faces or anvils of the jaws areaccurately ground and lapped so as to be exactly parallel as they cometogether.

To the lower jaw assembly 2, is also affixed a recording counter 10 ofany suitable well known type such as is actuated by the up and downmovement of a lever arm ll. When set to count the folds this lever armis held by a catch IQ of which a preferred form is shown in Fig. 2 as anenlarged view. As long as the strip is intact, the assembly 2 issuspended by the strip and the arm H remains in the hook I5, of thecatch, so that each time the assembly 2 is pushed up by the cam 8, thelever ll being held up in the hook of the catch l2, actuates the counter10. When the strip breaks, the assembly 2 being no longer supported,drops so as to bear continually upon the cam 8 so that in the lowestposition of the cam 8, the lever H drops sufiiciently to rest upon thebottom of the slot [5 in the catch and opposite the entrance IA. Thecatch being shaped substantially as shown, then falls over to the rightabout its hinge It thus releasing the lever arm II so that the counteris actuated no longer and so the number of revolutions of the cam andthus the number of folds from the time when the catch is set till thestrip breaks is recorded. The apparatus so far described will test thenumber of single folds which a specimen will withstand before breakingas, once a single fold has been made in a selected direction, thenatural resiliency of the specimen will ensure that the fold is repeatedin the same direction as the jaws move together in each cycle. If it isdesired to test the number of double folds which the strip willwithstand before breaking, then it becomes necessary to attach to theapparatus, some type of shuttle mechanism, a preferred form of which isalso illustrated in Fig. 1. To the shaft holding cam 8 is attachedgearing l1 driving cam l8 which rotates at a speed twice that of cam 8.Against the outer surface of cam I8 is pressed by means of spring 22 thelower end of a lever 20 which is pivoted at 2|. The upper end of thelever is forked and holds a pin IS in a strap 23 which slides inbearings 26. In the strap are two pins 24 and 25 which project beyondthe width of the test strip l, and these are caused by the mechanismdescribed to oscillate to and fro in a controlled manner according tothe surface contour of the cam l8, completing their cycle in a halfrevolution of cam 8.

In order to more clearly explain the action of the shuttle mechanism andthe working of the apparatus, Fig. 3, is a diagram of the relative 1position of the jaws 2 and 3 and the two pins 24 and 25 when cam 8 inFig. 1 is furthest from the bottom of the lower jaw assembly 2. As thecam 8 turns and commences to lift the lower jaw, as shown in Fig. 4, theleft hand pin pushes the test strip to the right and as described, bysuitably shaping the surface of the cam I8 the pin is made to move justfast enough but no faster than required to take up the slack in the teststrip caused by the approach of the jaws to each other, so as not to putany substantial stress upon the test strip and yet prevent it fromcommencing to bend in a direction opposite to that which the pin ismoving. As soon as the test strip is sufiiciently bent to ensure itscontinued bending in the required direction, the pin is withdrawnrapidly as is indicated in Fig. 5, so as to be clear of the lower jaw asit moves past it and meets the upper jaws as shown in Fig. 6. In Fig. 6the weight of the upper jaw has been taken by the lower and thepredetermined pressure is being applied to the crease. Ignmediatelyprior to contact by suitably shaping the contour of cam B the travel ofthe lower jaw preferably has been reduced to a very-small predeterminedspeed, for example, 3.2 mm. per second. The lower jaw assembly 3 is thenrapidly lowered and the right hand pin now approaches the strip asindicated in Fig. '7. In the position indicated by Fig. 8, the downwardspeed of lower jaw preferably is reduced to a very small predeterminedspeed, for example 3.2 mm. per second, until the strip is put under atension not appreciably greater than that corresponding to the weight ofthe lower jaw assembly. On the return of the lower jaw the right handpin now pushes the strip to the left as indicated in Fig. 9 and the pinis rapidly withdrawn to the right as shown in Fig. 10 while the lowerjaw rapidly moves upwards to reach the contact position indicated inFig. 11, and as the lower jaw moves downwards again the left hand pinapproaches the strip as shown in Fig. 12 and the cycle illustrated byFigs. 3 to 12 is repeated until the strip breaks.

So as to provide for cases where the initial fold on the test strip doesnot occur exactly in the middle, the anvils of one of or preferably boththe jaws 2 and 3 are recessed or slotted as shown at 21 Fig. 3 and theexcess slack in one side or other of the strip in the position shown byFig. 6 or Fig. 11 is accommodated in the rectangular slot withouttending to disturb the location of the initial folded crease.

It is obvious that any convenient number of test jaws may be mountedside by side operated by a single driving motor and all the associatedshuttle pins contained in an extension of the strap 23.

The apparatus described may be simply and easily standardized bychecking the weight of the jaw assemblies and the speeds of the lowerjaw when subjecting the crease in the strip to both tension andcompression, thus ensuring that every specimen tested in jaws of thesame or different pieces of apparatus are folded and treated in apositive and unvarying manner.

It will be noted that in the described method of carrying out the test,the action of the repeated folding together of a piece of paper, forexample, a currency note, applying pressure to the crease and thensubjecting the note to repeated tension upon unfolding it, is simulated,but under controlled conditions. In this respect also, it is superior totesting methods and apparatus hitherto used for this purpose.

Having thus described the nature of the invention I declare that what Iclaim is as follows:

1. The method of testing the folding endurance of a strip of materialwhich consists in folding it double about a line across its width;squeezing the strip together at the folded edge; unfolding the strip andsubjecting its ends to a predetermined tension, then folding the stripdouble in the reverse way to the previous fold about the same line,reapplying the squeezing pressure; unfolding the strip, reapplying thetension and continuing these steps successively until the strip breaksand recording the number of double folds so made before fracture.

2. An apparatus for testing the folding endurance of a strip of materialcomprising sets of jaws adapted to grip the ends of a strip of thematerial to be tested, means for continuously and successively bringingthe sets of jaws together, such movement causing the strip to be foldedacross its width; means for squeezing the end faces of the jaws togetherupon the fold; means for separating the jaws and applying an unvaryingpreselected tension to the unfolded strip by means of a freely hangingload, together with means for recording the number of cycles thuscompleted before the strip breaks.

3. In an apparatus for testing the folding endurance of a strip ofmaterial comprising, jaws adapted to grip the ends of a strip of thematerial to be tested, means for bringing the jaws together, suchmovement causing the strip to be folded across its width; means forsqueezing the ends of the jaws together upon the fold; means forseparating the jaws and applying a predetermined tension to the creasedstrip; means for successively reversing the direction of the fold aboutthe crease each time the jaws come together, together with means forrecording the number of cycles thus completed before the strip breaks.

4. In an apparatus for testing the folding en-- durance of a strip ofmaterial, two sets of jaws for gripping and holding the ends of thestrip to be tested in one plane, said jaws having on both sides of thestrip, pressure faces adapted for uniformly squeezing the resulting foldin the strip when they come together and the pressure faces in at leastone of the jaws recessed along the line where the strip is gripped so asto accommodate any slack in the test strip caused by unsymmetry as thestrip is folded and squeezed.

5. In an apparatus for testing the folding endurance of a strip ofmaterial a member having jaws for gripping one end of the strip, saidjaws having, on both sides of the. strip, surfaces for squeezing a foldformed in the strip against another member, said surfaces beingseparated by a gap.

6. In an apparatus for testing the folding endurance of a strip ofmaterial two sets of jaws adapted to grip the ends of a test strip,means for folding the strip about itself while in the jaws to form acrease, a load for applying through one set of jaws an unvarying tensionto the strip when unfolded, the sets of jaws being so mounted that thedistance between them is determined only by the length of the unfoldedstrip between the gripped edges while being subjected to'the saidtension.

\ JAMES DA. CLARK.

